In the month since Firefox 4's launch, the browser has racked up 100 million downloads, Mozilla said last weekend.

But statistics from one Web analytics company showed that Firefox 4's introduction has done nothing to boost Mozilla's overall share of the browser market.

The 100 million figure was touted by Asa Dotzler, Mozilla's community coordinator for Firefox marketing, in an entry on his personal blog Saturday. As of late Sunday, Firefox 4's download counter stood at 103 million.

According to Irish Web metrics company StatCounter, Firefox 4 downloads have translated into a usage share jump for that edition since its March 22 launch.

Through April 24, Firefox 4's average share for the month was 7.3%, more than double the average for March. In the past four days, its share has exceeded 8%.

But Firefox 4 has not changed Mozilla's total usage share: StatCounter's data has Firefox -- all editions, including Version 4 -- down three-tenths of a percentage point so far this month, consistent with the steady decline the browser has suffered since last fall.

Mozilla has yet to offer Firefox 3.6 users the upgrade to Version 4 -- that isn't scheduled to start until May 3 -- but from the numbers, all of Firefox 4's gains can be attributed to current users upgrading on their own. Firefox 3.6's March share of 24% tumbled to 19.2% this month, a 4.8-point loss that nearly matched Firefox 4's five-point gain during the same period.

While IE9 averaged a 2.1% share through April 24, and in the past several days climbed above 3%, its gains were not at the expense of rivals: StatCounter has all versions of IE down five-tenths of a point in April.

Firefox 4's larger gains aren't a surprise. The browser runs on Windows XP, Mac OS and Linux, all operating systems that IE9 does not support.

For that reason, Microsoft has argued that IE9 should be judged only by its gains on Vista and Windows 7, not all operating systems. Executives have also called Firefox-IE comparisons "premature at best ... misleading at worst" because of the differences in the browsers' upgrade mechanisms.

Microsoft began offering IE9 to Vista and Windows 7 users via Windows Update a week ago. Since then, IE9's share has increased a half percentage point over the previous week.

Firefox 4's market share has shot above 8% in the month since its launch, while IE9 has just cleared 3%. (Source: StatCounter)